Integrated class D audio amplifiers have been around for more than 10 years and steadily gained popularity due to numerous advantageous characteristics such as high power conversion efficiency, small dimensions, low heat generation and good sound quality. Bipolar CMOS and DMOS high voltage semiconductor processes are typical candidates for implementation of these integrated class D audio amplifiers which feature large LDMOS output devices as active switches of output stages. These LDMOS transistors are isolated high side devices and typically NMOS devices to minimize transistor dimensions for a given output resistance of the output stage. As the bipolar CMOS and DMOS high voltage semiconductor processes continue to evolve to feature sizes at 180 nm and below, the gate drive voltage required to the LDMOS active switches is approaching a voltage level around 5 V. This gate drive voltage should not be exceeded by the high side gate driver to maintain gate integrity by limiting the gate-source voltage of the high side LDMOS transistor to a voltage range that fits an oxide voltage range of the LDMOS transistor in question, such as the above-mentioned maximum of 5 V. This drive voltage accuracy requirement or constraint complicates the design of an adequate DC power supply voltage, i.e. the high side positive supply voltage, to the high side gate driver. Traditionally, the accuracy and stability requirements of the gate-source voltage applied to the high side LDMOS transistor have been accomplished by using an external bootstrap capacitor for the DC supply voltage of the high gate driver of every high side LDMOS transistor.
However, external capacitors typically add an unacceptable amount of component and assembly costs for numerous types of applications of the integrated class D audio amplifier, in particular low-cost high-volume consumer audio systems. A further drawback of this solution is that a typical Class D audio amplifier may include numerous high side power transistors and associated high side gate driver circuits each needing an external capacitor. This is for example the situation for H-bridge configured output stages of multi-level PWM amplifiers. Consequently, it is highly desirable to provide a novel high side gate driver and circuit capable of accurately driving a high side LDMOS transistor, and other types of high side power transistors, without any need for an external capacitor to stabilize the high side positive supply voltage for the high side gate driver. This has been accomplished by the present regulated high side gate driver circuit which comprises a novel type of a floating voltage regulator design providing an accurate and stable regulated supply voltage to the gate driver.